1. Field of the Invention
The present invention relates to a liquid crystal display (hereinafter referred to as an LCD), in particular, a liquid crystal display having a plurality of pixels with different storage capacitances.
2. Description of the Related Art
A thin film transistor (hereinafter referred to as TFT) LCD has a TFT as a switching element. The TFT LCD has a TFT array panel, a common panel and liquid crystal material therebetween. The TFT array panel includes a plurality of pixels each of which has a TFT and a pixel electrode, and the common panel includes a common electrode.
The LCD, particularly in twisted nematic (hereinafter referred to as TN) mode, has a narrow viewing angle and the optical transmission rate depending on the viewing angle. This dependence is due to the characteristics of the liquid crystal molecule and is greater upward and downward than right and left, causing the asymmetrical viewing characteristics.
In order to obtain a wider viewing angle, several approaches are suggested.
Kaneko et al. disclose several methods for obtaining wide viewing angle, in "Wide-Viewing-Angle Improvements for AMLCDs", SID 93 DIGEST pp. 265-268, such as film compensated TN cells, pixel divided TN cells, multi-domain TN cells, and TN cells using subpixels.
The TN cells using subpixels will be described with reference to FIG. 1A to 1C. A pixel is divided into three subpixels with different control capacitors C.sub.S2 and C.sub.S3. FIG. 1A is an equivalent circuit for the pixel with subpixels, FIG. 1B shows the plane structure of the pixel, and FIG. 1C shows the cross-sectional view of the pixel.
As shown in FIG. 1C, a gate electrode 2 is formed on a lower transparent substrate 1 and a first insulating layer 4 is deposited thereon. A first transparent electrode 5 is formed on the first insulating layer 4 and connected to a TFT. A second insulating layer 14 and a second transparent electrode 15 is formed on the part of the first transparent electrode 5, and a third insulating layer 24 and a third transparent electrode 25 is formed on the part of the second transparent electrode 15. A common electrode 10 is formed on a upper transparent substrate 9 opposite to the lower substrate 1.
The capacitance of a capacitor is inversely proportional to the distance between the electrodes of the capacitor and is proportional to the area of the electrodes. The conventional liquid crystal capacitor composed of a pixel electrode and a common electrode is divided into three liquid crystal sub-capacitors C.sub.LC1, C.sub.LC2 and C.sub.LC3. The sub-capacitors C.sub.LC1, C.sub.LC2 and C.sub.LC3 have the first, the second and the third transparent electrodes 5, 15 and 25 respectively as one electrode and the common electrode as the other electrode. Control capacitors C.sub.S2 or C.sub.S3 connected to the sub-capacitors C.sub.LC2 and C.sub.LC3 respectively in series act as voltage dividers and provide control voltages to the subpixels. The transparent electrodes 5, 15 and 25 are supplied with the same voltage, but the voltage V.sub.LCi applied between the two electrodes of the sub-capacitor C.sub.LCi (i=1, 2 and 3) are different from that of the other sub-capacitors. That is, the strength of the electric field applied into the liquid crystal in a subpixel is different from that in the other subpixels. In result, the pixel has domains with three different transmission rates and the resultant transmission rate of a pixel is the average value of the three transmission rates of the three subpixels. Therefore, the viewing characteristics of the LCD can be improved.
However, concerning the fabricating process, there is a disadvantage that the additional steps for forming the second and the third transparent electrodes, and the second and the third insulating layers.